An important function of making a 3D observation of a specimen is required for a device for examining a 3D specimen by use of charged-particle beams such as electron beams. When a specimen is subjected to 3D observation by use of an electronic microscope, the stage is tilted thereby to acquire a 3D image of the specimen. However, a mechanical operation is required for tilting the stage or column, which deteriorates throughput or reproducibility of tilt angle. As a method for making a 3D measurement of a specimen without tilting the stage, there is assumed that beams are tilted by use of a deflector. How ever, when beams are tilted (deflected) by a deflector, an aberration is generated and the beam diameter increases.
PTL 1 describes a technique capable of lowering energy when charged-particle beams pass through a corrector than energy when they pass through a lens whose chromatic aberration is to be corrected, thereby lowering a required specification for lens power supply stability, PTL 1 describes that beams with different energy are converged near the principal plane of a lens thereby to create an achromatic space on the image plane of the lens.